Why Do Cables Matter?

I’m a cable skeptic. Especially speaker cables. As long as they aren’t 20 gauge or something like that. But I am open minded. It could be that I just don’t know any better. That happened once before. Just once though.

I also suspect that most of it is psycho acoustics and doing an A B test is difficult because changing cables takes some time.

So my stupid question is this. What about just putting the "better, new, trial" cable on one channel, the old one on the other and then compare left / right with a mono source. For good measure switch sides after a while. Presumably the difference should be more readily heard.

I ask because right now I just have 12 g plain speaker wire. And perhaps relevant is that I’m using Magnepan LRS speakers that need a bit of current.  Oh and plain wire connection, no bananas.  

And the same thing for the phono to pre cables etc.  Just try one side first?

Is there some magical difference that occurs to the electricity after it comes out of the wall?   

Maybe that's the "special" electricity.  All the miles of electricity before the wall outlet doesn't matter.  We'll fix it at that last six feet before the amp.  

Power cables  are psychoacoustic nonsense.  Placebo effect and expectation bias.  The owners and sellers of these don't want to hear that.  Especially the sellers.

On the other hand, the placebo effect does work.

^  "I’m a dealer for Infigo audio."

I appreciate the honesty.